1. Field of the Invention
The present invention relates to an intake control device mounted in an intake air passage of an internal combustion engine, for controlling the quantity of air to be supplied into combustion chambers of the internal combustion engine by a throttle valve.
2. Description of the Prior Art
It is known in the art that in an intake control device for use in an internal combustion engine provided with a fuel injection system, a throttle body is connected to the upstream side of an intake manifold of the internal combustion engine in which a spherical wall surface is formed in an inner wall of the air passage of the throttle body at a position facing to the external circular edge portion of the throttle valve for controlling the effective surface area of the air passage, for the purpose of stabilizing the operation of the internal combustion engine within a range of low rotational speeds of the engine.
The throttle body shown in FIG. 3 has been disclosed in Japanese Patent Application Laid-Open Gazette No. 15631/1991, in which a body member 1 of the throttle body is formed in a cylindrical shape provided with an air inlet 2 on the upstream side and an air outlet 3 on the downstream side connected to an intake manifold (not illustrated); an air passage 4 is formed inside of the body member 1 to connect the air inlet 2 to the air outlet 3; and disk-like throttle valve 5 is positioned in the air passage 4 and rotatably supported to the body member 1 by a throttle shaft 6.
The throttle valve 5 is rotated, in accordance with the operation of an accelerator pedal (not illustrated), between a first position indicated by a solid line in FIG. 3, that is, a closed position of the air passage 4, and a second position indicated by a dashed line, that is, a wide-opened position of the air passage 4. The outer peripheral edge of the throttle valve 5 is divided by the throttle shaft 6 as a boundary into a first external circular edge portion 5a which moves toward the upstream side of the air passage 4 and a second external circular edge portion 5b which moves toward the downstream side when the throttle valve 5 rotates from the first position toward the second position.
When the throttle valve 5 is in the first position, the first external circular edge portion 5a and the second external circular edge portion 5b of the throttle valve 5 are located at positions almost in contact with an inner wall 7 which defines the air passage 4 of the body member 1, respectively. The inner wall 7 of the body member 1 is provided with an upstream-side spherical wall surface 8 which is formed protrusively into the air passage 4 on the upstream side from a portion of the inner wall 7 facing to the first external circular edge portion 5a, and also a downstream-side spherical wall surface 9 which is formed protrusively into the air passage 4 on the downstream side from a portion of the inner wall 7 facing to the second external circular edge portion 5b. The upstream-side spherical wall surface 8 and the downstream-side spherical wall surface 9 terminate in positions where the throttle valve 5 has rotated by a predetermined angle from the first position, respectively. The upstream-side spherical wall surface 8 and the downstream-side spherical wall surface 9 are formed in such spherical surfaces that, clearances between the spherical wall portions 8 and 9 and the first and the second external circular edge portions 5a and 5b of the throttle valve 5 increase with an increase in the angle of counterclockwise rotation of the throttle valve 5 from the first position, as indicated by a dot-dash-line in FIG. 3. Accordingly, a rate of increment in the quantity of air to be supplied into the intake manifold of the internal combustion engine remains small during the movement of the external circular edge portions 5a and 5b of the throttle valve 5 along the spherical wall surfaces 8 and 9; when the external circular edge portions 5a and 5b of the throttle valve 5 have moved as far as a position off from the spherical wall surfaces 8 and 9, the rate of increment in the quantity of air supplied into the intake manifold of the internal combustion engine becomes large. In the low-speed and medium-speed ranges of the internal combustion engine, therefore, a slight variation in the angle of rotation of the throttle valve 5 stabilizes engine operation without causing a variation over a target value in the rate of increment in the quantity of air supplied into the intake manifold. In the high speed range, the rate of increment in the quantity of air supplied into the intake manifold can be made high as compared with the rate of increment in the angle of rotation of the throttle valve 5.
When the throttle valve 5 is moved back to, or near to, the first position, with the accelerator pedal released or loosened, during the operation of the internal combustion engine in a high-speed range, the vacuum in the intake manifold, that is, the intake manifold vacuum, increases and accordingly the throttle valve 5 is pulled toward the air outlet 3 located on the downstream side, resulting, at this time, in deflection of the throttle shaft 6 and looseness of the pedestal supporting the throttle shaft 6 to the body member 1. Thus the throttle valve 5 moves toward the air outlet 3 on the downstream side, sometimes causing the second external circular edge portion 5b of the throttle valve 5 to contact the downstream-side spherical wall surface 9. If this contact occurred, there would occur resistance with the rotation of the throttle valve 5 in the direction in which the quantity of air flowing in the air passage 4 increases, disturbing smooth operation of the internal combustion engine.